In the course of time, the stability of a gas-filled proportional counter requires, among other things, that the composition of the gas phase remains unchanged. However, the gas phase composition tends to change for various reasons. For instance, the different materials which the proportional counter is made of gradually emit gases absorbed in their surfaces; gases trapped in the pores of the materials also continuously flow into the gas filling. Moreover, small leakages from the window and/or the jointings of the proportional counter cause changes in the gas phase composition. Thus the properties of the whole proportional counter easily change if any impurities enter the gas phase.
The conventional methods for manufacturing proportional counters aim at achieving a steady stability for the gas phase by means of pumping the counter, i.e. the detector, for a long time before filling, and by heating it simultaneously. This method is not, however, completely secure in eliminating all possible sources wherefrom the gas filling can in the course of time be contaminated.
In the prior art, gas phase stabilizers operated in room temperature have been developed to eliminate the gases emitted in various vacuum tubes. Noble gases are chemically completely inert, and therefore the same stabilizers, the getters, can be employed for maintaining the purity of the noble gas filling.
It is, however, necessary to activate the gas stabilizers, i.e. the getters, before they can bind impurities. The activating is normally carried out by heating the stabilizer in a vacuum up to the temperature of 500.degree.-800.degree. C., while the activating time depends on the required temperature.
The commonest methods for activating the gas phase stabilizer of a proportional counter are resistance heating and high-frequency heating. Resistance heating requires that an extra electric inlet is installed within the proportional counter, which adds the complexity of the proportional counter structure, and thus increases its manufacturing costs. High-frequency heating is out of question if the gas phase stabilizer, the getter, must be located essentially within a counter which is altogether made of metal. Moreover, the heating of the whole counter in order to activate the stabilizer is impossible, because the jointings used in manufacturing the counter do not, as a whole, endure the high temperature required in the heating.
The purpose of the present invention is to eliminate the drawbacks of the prior art and to achieve a method, both better and more secure in operation than the prior art methods, for heating the gas phase stabilizer so that the stabilizer can be activated and thereafter employed for eliminating the impurities emitted into the gas filling.